Arc ignition circuit



w. E. BAHLS ARC IGNITION CIRCUIT Aug. 4, 1942;

Filed Ndv. 26, 1958 2 sheets-sheet 1 Lbad Control fbiential ControlPotential WI'TNESSES: QINVENTOR 'WaZtErEBafiZS.

ATTORN Au 4, 1942. w. E. BAHLS 2,

ARC IGNITION CIRCUIT Filed Nov. 26. 193B 2 Sheets-Sheet 2 Load Fzj 3.

Load 7 Control Etc/dial Fig.4.

WITNESSES; LIQNVENTOR WaZfrEBa/vls. WWWM I "7%, ATTORN Y Patented Aug.4, 1942 2,292,034 ARC IGNITION CIRCUIT Walter E. Bahls, Verona, N. Jassignor to West= inghouse Electric & Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application November 26,1938, Serial No. 242,487

11 Claims.

My invention relates to electric discharge apparatus and has particularrelation to ignition circuits for discharge devices of theimmersedignition-electrode type.

A discharge device of the immersed-ignitionelectrode typecomprises, ananode of nickel, carbon or other suitable material, a mercurypoolcathode and an ignition electrode of a high resistance material such asboron carbide or silicon carbide. To render the discharge deviceconductive, a current of substantial magnitude is transmitted betweenthe ignition electrode and the mercury-pool cathode. For a device ofmoderate rating, the current transmitted may be of the order of 10amperes. Since the resistance of the ignition electrode is relativelyhigh, the potential required to transmit the current is substantial. Forthe 10 ampere ignition electrode, the power required is of the order of2000 watts.

In view of the large magnitude of the power required in rendering adischarge device conductive, it isessential that the ignition currentflow for as short a time as possible. If the starting current flows fora substantial interval of time, the ignition electrode becomes heated toa relatively high temperature and is seriously damaged.

In accordance with the teachings of the prior art, of which I am aware,the ignition electrode is connected to the anode of the discharge devicethrough an auxiliary valve. To render the main device conductive,current is supplied through the auxiliary valve and the ignitionelectrode. As soon as the main arc strikes, the ignition current isinterrupted, since the potential drop across the auxiliary valve and theignition electrode is equal to the main arc drop and this potential istoo small to maintain current flow through the auxiliary valve.

In many situations, it is inconvenient to use the above described priorart ignition circuit. In such cases, what may be designated asindependent ignition is applied. An independent ignition circuit, as thename implies, is supplied from an independent source and the connectionto the anode of th main device which makes possible the decrease in theignition current is no longer available. In this case, it is, of course,

also important that the current fiowthrough the ignition electrode bediscontinued as soon as it has performed its function.

' It is accordingly an object of my invention to provide an independentignition circuit for a discharge device of theimmersed-ignition-electrode operate with a minimum expenditure of energyfor a discharge device of the type in which substantial current isrequired between the ignition electrode and one of the principalelectrodes.

An ancillary object of my invention is to provide a novel oscillationgenerator of the type that supplies a saw-tooth wave form.

More concisely stated, it is an object of my invention to provide anindependent ignition circuit that shall operate without causing damageto the ignition electrode or the other associated elements of anelectric discharge device.

According to my invention, I provide an ignition circuit in which, byone means or another, the ignition current is quickly extinguished afterit has performed its function. This may be accomplished by supplying theignition current through an auxiliary valve and providing a secondauxiliary valve which is rendered conductive in response to the flow ofthe main current, to short circuit the first auxiliary valve and theignition electrode. The same object may also be accomplished bysupplying the ignition current through an auxiliary valve and acapacitor in series. In this case, the capacitor may function toextinguish the auxiliary valve and interrupt the flow of current after ashort time. same purpose, a charged capacitor may be quickly dischargedand recharged through the ignition electrode and an auxiliary valve. Inthe above described ignition circuits, the flow of current need notpersist for an interval of time longer than one or two microseconds,sinc it need fiow for only this interval to render the main valveconductive.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich Figure l is a diagrammatic view showing an embodiment of myinvention;

Fig. 2 is a diagrammatic view showing a modification of my invention;

Fig. 3 is a diagrammatic view showing another modification of myinvention; and

For the Fig. 4 is a diagrammatic view showing a further modification ofm invention.

The apparatus shown in Fig. 1 comprises a discharge device 5 of theimmersed-ignition-electrode type having an anode I, a cathode 9 and anignition electrode II which dips into the cathode. Anode-cathodepotential is impressed on the discharge device from a source ofalternating current I3 through a supply transformer I5 and when thedischarge device is rendered conductive, current flows through whateverload I! is to be energized.

To render the discharge device 5 conductive, current of substantialmagnitude is supplied between the ignition electrode II and the cathode9. For this purpose, the ignition electrode and the cathode areconnected in series with an auxiliary discharge device I9, a pair ofresistance elements 2I and 23 and the secondary section 25 of anauxiliary transformer 21. The latter may be, as indicated, supplied froma source 29 independent of the main source I3. On the other hand, thesecondary section 25 may be a section of the main transformer I5.

The auxiliary discharge device I9 is of the arelike discharge typehaving an anode 3 I, a cathode 33 and a control electrode 35 and asuitable gaseous or vaporous medium. To determine its operation acontrol device 31 of any well known type is provided. When the auxiliarydevice I9 is rendered conductive, current flows through it, the ignitionelectrode II and the cathode 9 of the main device 5, and the latter isrendered conductive. The current fiow through the ignition electrode IIneed only persist for an interval of time of the order of severalmicro-seconds to perform its function. After this, there is no longerany necessity to continue the current flow and to save power and preventthe ignition electrode from being damaged, the ignition current flow isinterrupted.

For this purpose, a second auxiliary discharge device 39 is connectedacross the series circuit comprising one of the resistors 2|, the anode3| and the cathode 33 of the first auxiliary discharge device I9, theignition electrode I I and the cathode 9 and is thus supplied from theauxiliary secondary 25. The second auxiliary device 39, like the firstdevice, is of arc-like type and comprises an anode 4|, a cathode 43, acontrol electrode I5, and a gaseous medium. It is rendered conductive inresponse to the fiow of load current through the main discharge device5.

The change produced in the load circuit by current fiow through the loadI! is transferred to the auxiliary device 39 through another auxiliarytransformer 41. The primary 49 of the transformer is connected in serieswith the load I1 and the anode I and cathode 9 of the main device 5. Thesecondary 5| of the transformer 41 is connected across a resistor 53through a rectifier 55 which may be of the dry coppercopper-oxide type.The terminal 51 of the resistor 53 which becomes positive when currentflows through the rectifier 55 is connected to the control electrode 45of the second auxiliary device 39. The other terminal 59 of the resistoris connected to the cathode of the second auxiliary device through abiasing source 6| which normally applies a negative potential betweenthe control electrode 45 and the cathode 43 of the device to maintain itnon-conductive. When current flows through the main discharge device 5,the auxiliary transformer 41 in its main circuit supplies unidirectionalcurrent through the resistor 53 and a potential is impressed between thecontrol electrode 45 and the cathode 3 oi the auxiliary device 39 whichis suflicient to counteract the effect of the biasing source CI and torender the auxiliary device conductive. Under the action of thepotential drop through the ignition electrode II and the impedance II inseries with the first auxiliary device I9, current now flows through thesecond device 39 and the potential across the first auxiliary device I9,its series impedance 2| and the ignition electrode II is reduced to thearc drop across the second device 39. The first device is thereforerendered non-conductive and the fiow of current through the ignitionelectrode is discontinued.

The second auxiliary device 39 now remains conductive as long as theanode-cathode potential impressed thereon is suflicient to maintain theare. When this potential becomes too small to maintain the discharge,the second device becomes non-conductive and the apparatus is reset foranother operation if one is necessary or desirable. Where the maindevice 5 and the auxiliary devices I9 and 39 are supplied from the samesource, or from sources of the same frequency, the second auxiliarydevice may be rendered non-conductive substantially at the same time ora short time before the main device is extinguished. After this, thethree discharge devices remain non-conductive until the first auxiliarydevice I9 is again rendered conductive and as a consequence, the maindevice 5 isrendered conductive and causes the second auxiliary device 39to become conductive and deenergize the first device.

In the apparatus shown in Fig. 2, the ignition current is supplied fromthe auxiliary secondary 25 through the series circuit including acapacitor 63, an auxiliary discharge device 55, the' ignition electrodeI I and the cathode 9 of the main device 5. The auxiliary dischargedevice 65 is of the arc-like type comprising an anode 61, a cathode 69,and a control electrode II. A resistor 13 is connected in parallel withthe capacitor 53 to discharge it when it has been charged. The magnitudeof the resistor I3 is such that continuous current fiow through it andthe auxiliary discharge device 65 is not suflicient to cause damage tothe ignition electrode.

To ignite the main discharge device 5, the proper potential is suppliedbetween the control electrode II and the cathode 69 of the auxiliarydevice 65 to render it conductive. Current then flows through thecapacitor 63, the auxiliary device 65 and the ignition electrode II andthe cathode 9 of the main device 5 and the capacitor becomes chargedwith the plate I5 connected to the anode 61 of the auxiliary devicenegative and the other plate 11 positive. The properties of thecapacitor 63 and the auxiliary device 35 are such that the current flowis suflicient to render the main device 5 conductive. The relationshipbetween the capacitor 53, the auxiliary device 65 and the ignitionelectrode II is such that the capacitor is thereafter quickly charged toa potential such that the auxiliary device 55 is quickly extinguished.After the latter event, the main device 5 continues to "carry currentwhile no current flows through the ignition electrode II until thecapacitor 03 has been suii'.l ciently discharged to permitreenergization of the auxiliary device 65. Preferably, the dischargingresistor I3 is so dimensioned that this does not occur for substantiallyas whole period of the main source I3, since it is undesirable thatcurrent-be conducted through the ignition electrode H until such currentis necessary and the ignition current flow is only necessary when themain device is again to be rendered conductive.

In the Fig. 3 modification, the ignition circuit also includes acapacitor 19 and an auxiliary discharge device 8| of the arc-like typehaving an anode 83,21 cathode 85 and a control electrode 87. In thiscase, one plate 89 of the capacitor 18 is connected to the terminal 9!of the main secondary section 93 of the supply transformer 95 to whichthe anode I of the main device 5 is connected through the load H. Theother plate 91 of the capacitor I9 is connected to the ignitionelectrode ll through the anode 83 and the cathode 85 of the auxiliarydischarge device fill. The capacitor is first charged with its lowerplate 91 positive and its upper plate 89 negative from another secondarysection 99 of the transformer 95 through the rectifier NH. The sections93 and 9d of the transformer 95 are so wound that the charging of thecapacitor l9 occurs during the half period during which the anode l oithe main device 5 is negative and the cathode is positive.

When the main device 5 is to be rendered conductive, suitable controlpotential is supplied to the auxiliary device 88 and the latter isrendered conductive when the potential of the secondary section 93 is ofproper polarity. Current now flows. from the main winding 93 of thesupply transformer 95 through the auxiliary device it and the ignitionelectrode 9! and the cathode 9 g of the main device to discharge thecapacitor and recharge it to the opposite polarity. The current flow issuficient to render the main device conductive. Moreover it persists foronly a short'interval of time, since by reason of the iact that theresistance in series with the capacitor is small, the latter sooncharges to a potential tending to extinguish the auxiliary device iii.At the same time no current flows through the rectifier EM to charge thecapacitor iii since the potential of secondary section iii-l is suchthat the rectifier Mi blocks current flow. When the potential suppliedby the main secondary section 533 and the section 99 subsequentlyreverse in polarity current again flows through the rectiiier tilt toagain discharge the capacitor J9 and recharge it to the first polarity.The latter operation need not take place at the same rate as theignition operation, and, therefore, a resistor M13 is connectedin serieswith the rectifier. It is to be noted that if the resistor is of propermagnitude, the discharge and recharge of the capacitor 79 through therectifier Mil may take place relatively slowly while the discharge andrecharge through theauxiliary device 86 may take place quickly. The waveform produced by the charging and discharging of the capacitor is thusof the saw-tooth type.

The modification of my inven'ion shown in Hg. 4 is similar to that shownin Fig. 3 except that the auxiliary secondary section 99 of the maintransformer is omitted. The capacitor 79 is in this case charged fromthe main section 93 of the supply transformer through the rectifier Ml.For this purpose, the lower plate iii of the capacitor is connected tothe cathode terminal I05 of the secondary section 93 through therectifier WI." The capacitor 119 is now charged during the half periodsduring which the. main anode-cathode potential is negative anddischarged and. recharged to the opposite polarity during the positiveanode-cathode periods of the source.

My invention has been shown herein as applied specifically to adischarge device of the immersed ignition electrode type. While it haspeculiar advantages when used with a discharge device of this type, itmay also be used with discharge devices in which the ignition electrodeis spaced a short distance from the cathode and a make-alive arerequiring substantial current is ignited. Where the essence of myinvention is applied with discharge devices of this type, it is intendedthat the use shall fall within the scope thereof.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

I claim as my invention:

1. In combination, a main electric discharge device having a pluralityof principal electrodes and an ignition electrode disposed adjacent oneof said principal electrodes, current of substantial magnitude beingrequired between said ignition electrode and said one principalelectrode to render said device conductive, a current path for supplyingignition current between said ignition electrode and said one principalelectrode and means. including an auxiliary electric discharge deviceconnected to be rendered conductive in response to the conduction ofcurrent through said main electric discharge device, for interruptingcurrent how in said current path.

2. In combination, a main electric discharge device of the immersedignition electrode type having a plurality of principal electrodes andan ignition'electrode disposed in contact with one of said principalelectrodes, current of substantial magnitude being required between saidignition electrode and said one principal electrode to render saiddevice conductive, a current path for supplying ignition current betweensaid ignition electrode and said one principal electrode, and meansincluding an auxiliary electric discharge device connected to berendered conductive in response to the conduction of current throughsaid main device, for interrupting the current flow in said path.

3. In combination, a main electric discharge device having a pluralityof principal electrodes and an ignition electrode disposed adjacent oneof said principal electrodes, current of substantial magnitude beingrequired between said ignition electrode and said one principalelectrode to render said device conductive, a current path including afirst auxiliary electric discharge device of the arc-like type, forsupplying ignition current between said ignition electrode and said oneprincipal electrode and means, including a second auxiliary electricdischarge device connected to be rendered conductive in response to theconduction of current through said main electric discharge device, forinterrupting current flow in said current path.

4. In combination, a main electric discharge device having a pluralityof principal electrodes and an ignition electrode disposed adjacent oneof said principal electrodes, current of substantial magnitude beingrequired between said ignition electrode and said one principalelectrode to render said device conductive, a current path including afirst auxiliary electric discharge device of the arc-like type,impedance means and means for causing current to flow through said firstdevice and said impedance means in series for supplying ignition currentbetween said ignition electrode and said one principal electrode andmeans, including a second auxiliary electric discharge device of thearc-like type in parallel with said first device and said impedancemeans, connected to be rendered conductive in response to conduction ofcurrent through said main electric discharge device, for interruptingcurrent flow in said current path.

5. In combination, a main electric discharge device of the immersedignition electrode type having a plurality of principal electrodes, andan ignition electrode disposed in contact with one of said principalelectrodes, current of substantial magnitude being required between saidignition electrode and said one principal electrode to render saiddevice conductive, a current path for supplying ignition current betweensaid ignition electrode and said one principal electrode, including theseries circuit consisting of a source of current, impedance means. afirst, auxiliary discharge device of the arc-like type, said ignitionelectrode and said one principal electrode, and means including a secondauxiliary electric discharge device of the arc-like type in parallelwith said first device, said impedance means, said ignition electrodeand said one principal electrode connected to be rendered conductive inresponse to the conduction of current through said main device, forinterrupting the current flow in said path.

6. In combination, a main electric discharge device having a pluralityof principal electrodes and an ignition electrode disposed adjacent toone of said principal electrodes, current of substantial magnitude beingrequired between said ignition electrode and said one principalelectrode to render said device conductive, a current path for supplyingignition current between said ignition electrode and said one principalelectrode, said path comprising a capacitor, an auxiliary electricdischarge device of the arc-like type connected in series with saidignition electrode and said one principal electrode and a source ofalternating current for charging said capacitor through said seriesconnected elements, means for rendering said auxiliary device conductiveso that said capacitor is charged, and means for discharging saidcapacitor, said capacitor being of such magnitude that when saidauxiliary device is rendered conductive, it is charged sufllciently torender said auxiliary device non-conductive in an interval oi time thatis short compared to a half period of said source and said dischargingmeans being such that said capacitor is discharged sufliciently so thatsaid auxiliary device may be again rendered conductive duringsubstantially a period of said source.

7. In combination, an electric discharge device having a plurality ofprincipal electrodes and an ignition electrode disposed adjacent to oneoi! said principal electrodes, current 01 substantial magnitude beingrequired between said ignition electrode and said one principalelectrode to render said device conductive, a capacitor, means forcharging said capacitor to one polarity and a current path for supplyingignition current between said control electrode and said one principalelectrode including a source of potential having one terminal connectedto said one principal electrode and the other terminal to one plate ofsaid capacitor, and means for discharging said capacitor and rechargingit to the opposite polarity, said discharging and recharging meansincluding means for connecting the other plate of said capacitor to saidignition electrode.

8. In combination, an electric discharge device having a plurality ofprincipal electrodes and an ignition electrode disposed adjacent to oneoi said principal electrodes, current of substantial magnitude beingrequired between said ignition electrode and said one principalelectrode to render said device conductive, a capacitor, means,including a first source of potential, for charging said capacitor toone polarity, a current path including a second source of potential forsupplying ignition current between said control electrode and said oneprincipal electrode, said second source having one terminal connected tosaid one principal electrode and the other terminal to one plate of saidcapacitor, and means for discharging said capacitor and recharging it tothe opposite polarity, said discharging and recharging means includingmeans for connecting the other plate of said capacitor to said ignitionelectrode.

9. In combination, a capacitor, means including a first source ofpotential for charging said capacitor to one polarity, a work circuitincluding said capacitor, a second source of potential in said circuit,and a discharge device of the arc-like type for controlling the flow ofcurrent through said circuit, said device and second source beingeffective to discharge said capacitor through said circuit and rechargeit to the opposite polarity.

10. In combination, a capacitor, means including a source of directcurrent potential for charging said capacitor to one polarity, a workcircuit including said capacitor, a source of alternating currentpotential in said circuit, and a discharge device of the arc-like typein said circuit for controlling the flow of current therethrough, saiddevice and alternating current potential source being effective todischarge said capacitor through said circuit and recharge it to theopposite polarity.

11. In combination, a capacitor, means including a source of directcurrent potential for charging said capacitor to one polarity, a workcircuit including said capacitor, a source of alternating currentpotential in said circuit, and a discharge device of the arc-likeasymmetric type in said circuit and having its anode connected to theplate of said capacitor that is charged positive, said device andalternating current source of potential being effective to dischargesaid capacitor through said circuit and recharge it to the oppositepolarity.

' WALTER E. BAHLS.

